1. Field of the Invention
The present invention generally relates to forming a robust intermetallic via structure. In particular, the present invention is directed to creating a pyramiding via structure that allows for a gradual rise in temperature from one end to the other. This minimizes the effects of abrupt thermal gradients and related stress effects.
2. Description of the Prior Art
A back-end of line (BEOL) process is generally associated with a layer of metal which is deposited on a wafer to electrically connect active components, such as transistors or resistors, by wiring on the wafer. When high currents pass through the BEOL device, a temperature profile naturally develops due to the thermal energy coming from the Joule heating caused by the high current. Some electric connection media in the BEOL devices, such as vias, are made of tungsten (W) or other highly resistive contacts which are especially subject to the high Joule heating derived from such high currents.
As a result, the temperature developed within the BEOL devices, and within the vias in particular, is significantly higher than within the surrounding metals. This difference in temperature among the metal elements creates an abrupt temperature spike within the vicinity. This brings forth many reliability problems.
One problem is the potential failure of the BEOL device due to the sudden breakdown of the structure. A second problem is delamination of the structure due to stress created by the thermal expansion of the uneven temperature spike within the vicinity. This may bring forth yet another problem: the delamination of the structure will cause torsion and cracking of the entire structure, which makes the weak BEOL devices even more unreliable.
In light of the above, a novel interconnect structure is needed to overcome the problem of the abrupt temperature spike within the vicinity due to high current passing through highly resistive materials.